Objective.To evaluate the association between sleep and wakefulness duration and childhood unintentional injury.Study Design.Case-crossover study.Methods.Two hundred ninety-two injured children who presented at the Children's Emergency Center of Udine, Italy, or their parents were interviewed after a structured questionnaire. Information was collected concerning sociodemographic variables, participant's habits, and injury characteristics, including a brief description of the accident dynamics. Sleep or wakefulness status of the child was assessed retrospectively for each of the 48 hours before injury. For each child, we compared the 24 hours immediately before the injury (hours 1–24; case period) with hours 25 to 48 (control period). Nonparametric tests were conducted to compare the difference of sleep duration between case and control periods. In addition, we conducted intrapersonal conditional logistic regression analyses and estimated relative risks (RRs) and 95% confidence intervals (CIs).Results.Overall, more children had longer hours of sleep during the control period than during the case period. However, this difference was significant for boys only. A direct association between injury risk and sleeping <10 hours was found among boys (RR: 2.33; 95% CI: 1.07–5.09) but not among girls (RR: 1.00; 95% CI: .29–3.45). This association was particularly strong among boys attending nursery school. We also found a direct association between injury occurring between 4 pm and midnight, and being awake for at least 8 hours before injury occurred (both sexes, RR: 4.00; 95% CI: 1.13–14.17).Conclusions.Our findings show that inadequate sleep duration and lack of daytime naps are transient exposures that may increase the risk of injury among children. These results suggest new prospects for injury prevention in childhood. children, injury, sleep, case-crossover, epidemiology.